Process of producing metal powder from metal carbonyl



Dec. 13, 1955 A. G. RAMSAY El AL 2,726,951

PROCESS OF PRODUCING METAL POWDER FROM METAL CARBONYL Filed July 29, 1952 Inventor: ALEXANDER G. RA MSAY ALBERT E. WALLIS y attorney United States Patent PROCESS OF PRODUCING METAL POWDER FROM METAL CARBONYL Alexander Gray Ramsay, -Coniston, Clydach, and Albert E. Wallis, Clydach, Great Britain, assignors to The International Nickel Company, Inc., New York, N. Y.

Application July 29, 1952, Serial No. 301,562

Claims priority, application Great Britain July 30, 1951 9 Claims. (Cl. '75.S)

This invention relates to processes for the production of metal powder by thev decomposition of metal carbonyl. It is known that when metal carbonyls (particularly those of nickel and iron) are. thermally decomposed to yield metal powders, the nature of the metal powder may vary from dense discrete particles to a much lighter fiocculeut form in which the metal powder has a fibrous or hair-like structure of much lower bulk density, lying between 0.3 and 1.3 grams per cc. purposes such a fibrous product is required, and as arule its bulk density must lie within critical limits, e. g.,.

0.7 to 0.9 gram per cubic centimeter.

The decomposition of carbonyl vapour is highly endothermic. We have observed that the nature of the decomposed product varics with the speed of decomposition and the concentration of the carbonyl vapour, which may be diluted with carbon monoxide. It is. bclievedthat if the vapour is highly concentrated and rapidly decomposed, a large number of small nuclei are formed initially and subsequently unite to form thin threads. If, however, the rate of decomposition is slow, the comparatively small. number of nuclei first formed build up into larger discrete particles. Naturally there is no clearcut division between the two kinds of particles; but rather, as the rate of decomposition and the concentration of the vapour increase, there is an increase in the number of thin threads.

The rate of decomposition varies. with both the temperature and the speed of How of the vapour. If a high rate of flow, i. e., a high rate of input of carbonyl vapour, is used in the standard form of decomposer in order to reduce the bulk density of the product, it is very difiicult to ensure that all the product will be of the desired density. Small changes in the rate of input or of the temperature lead to substantial changes in the density. The dithculty of controlling the reaction to produce an end product of constant density stems from the highly endothermic nature of the reaction. A high carbonyl input requires a large amount of heat to decompose it, with the result that the walls quickly get coated with a thick adherent layer of powder which acts as a barrier to the flow of heat. undecomposed and flows down the middle of the vessel away from the hot Walls and may escape decomposition altogether or give rise to the wrong type of powder. Moreover, the operator works on readings given by a pyrometer; and with a high rate of input the pyrometer also gets caked up with the powder and gives false readings, so that the operator no longer knows the true conditions inside the decomposer.

The standard form of decomposer is a cylindrical chamber 3 feet or more in internal diameter. It is possible to produce a fibrous powder in this, but only by making the input of carbonyl vapour very high, that is, of the order of 'litres of liquid carbonyl per hour per foot of the circumferential length of the decomposition chamber; and then it is very clifficult to control the reaction. If, on the other hand, a much smaller decomposer is used,

For some industrial I Some of the carbonyl then remains.

2,726,951 Patented Dec. 13, 1955- the output of product is necessarily low, even it a rate of input is maintained which is high relative to the size of the decomposer.

It is an object of this invention to decompose metal carbonyl to yield a fibrous powder at a commercial rate without encountering operating difficulties.

It is another object to introduce highly concentrated carbonyl vapour close enough to a heated. decompose: wall to ensure the production of a fibrous product oi uniform quality.

Other objects will appear hereinafter.

In our invention. we. use alarge decomposition chamber, that is to say, one in which the cross-sectional is. at least 5 square feet; but. instead of making: of

. the standard cylindrical form, we make it of. elongated cross-section (e. g.,. annular or rectangular) of constant width. The carbonyl vapour which we introduce into this chamber is highly concentrated, that is to say. the concentration is. at least 65%, and preferably and we so introduce this concentrated vapour that during at. least the initial part of the decomposition the vapour is in contact. with, or no more than 15 inches from, a heated wall. If the distance of the vapour from a heated wall is considerable, for example, 20- or more inches, then the vapours become internally diluted by convection currents and by carbon monoxide resulting from gradual decomposition, which is unfavorable to the production of. fibrous nickel or iron powder of critical bulk density.

All the. walls of the decomposition chamber may be heated, though this is not necessary if the. vapour is introduced close to one. of the main walls and the width of the chamber is small. Any unheated wall soon becomes hot, particularly if it is the inner wall of an annular chamber- By means of this invention we bring about rapid decomposition to provide the desired concentration of small nuclei. By working in this way we. do not need to use. a high rate of input; but instead we can and do use a moderate rate, namely, one. equivalent to from 4 to 10 litres of liquid carbonyl per hour per foot of the length of the heated wall on. if all the walls are heated, of the sum, of their lengths.. This vapour is introduced through a series of nozzles spaced apart from one another over the length of the cross-section of the chamber.

It is difiicult to specify the exact decomposition temperature; but if the temperature in the chamber is measured in the conventional way by a pyrometer between 18 and 24 inches from the top of the chamber and 6 inches from. the heated wall, it is found that excellent decomposition is obtained if the pyrometer reads between 28.0 and 320 C. To obtain this temperature the wall or walls should be heated to about 400 C. Although higher temperatures. would bring about more rapid decomposition, they would also entail the well-known disadvantage of decomposition. of the carbon monoxide produced by the decomposition of the carbonyl.

Preferably,. the decomposition chamber is annular, and the preferred form of apparatus with an annular chamber is shown diagrammatically in the accompanying drawings, in which- Figure 1 is a sectionalelevation of the apparatus;

Figure 2 is a plan showing the distribution of the vapour inlets; and

Figure 3 shows one vapour inlet on a larger scale.

The apparatus shown comprises a decomposition chamher 1 having an outer cylindrical wall 2 and an inner wall 3 formed by a central tube closed at both ends. The chamber is surrounded by a heating jacket 4 supplied with hot line gases through inlets 5 and 6, these gases leaving at the bottom through an outlet 7. The carbonyl vapour is introduced through six nozzles 8 connected to a header 9 (not shown in Figure 2). The powder formed ing chamber 10, in which it is propelled by conveyor flights 11 to a discharge outlet 12. The carbon monoxide produced also enters the chamber and is removed by way of a pipe 13 and filter 14.

- In the apparatus shown in the drawings the radial width of the annular chamber around the tube 3 should not exceed 24 inches nor be less than 10 inches so as to provide 'a total cross-sectional area suflicient for large-scale production. For instance, the annular part of the chamber-maybe 3 feet 3 inches in outer diameter and 13 inches in internal diameter. The height of the chamber may be that of a usual decomposition chamber, say 8 to 10 feet. The axial length of the tube 3 is not critical. It must extend low enough to ensure that the decomposition is substantially completed in the annular space of which it forms the inner wall. It may extend as far as is indicated by the dotted lines 3, but satisfactory results are obtained if it has only the length indicated in full lines. a The vapour inlets 8 each consist of a tubular part 15 leading to a flaring part 16, substantially rectangular in cross-section, arranged to discharge the vapour close to and over'a substantial circumferential area of the wall 2.

In one decomposer of the type illustrated the decomposition chamber had an outer diameter of 3 ft. 3 inches and an inner diameter of 13 inches and a height of 10 ft. The outer wall of the chamber was heated by jets burning hot the gases from a producer gas furnace to give a reading of 280 to 320 C., on a pyrometer placed 18 inches from the top of the chamber and 6 inches from the out side wall. Nickel carbonyl vapour at 100% concentra-' tion was introduced into the chamber at the rate of 100 litres of liquid carbonyl per hour, that is, at a rate of 9.8 litres per hour per foot of the length of the heated wall; and the decomposition produced a fibrous powder of nickel having a bulk density of 0.75 gram per cc.

. Another'suitable cross-sectional shape of the decomposition chamber is rectangular, the width of the rectangle when all the walls are heated being not greater than inches but preferably being at least 20 inches. The length of the rectangle is not critical, but is preferably several times the width; and it may be, for instance, 6 feet.

In a rectangular decomposition chamber preferably all the walls are heated and carbonyl vapour is introduced through inlets equidistant from the long walls.

The bulk density of the powder may be controlled either by varying the temperatures within'the decomposer or preferably by the controlled dilutionof' the carbonyl vapour with carbon monoxide. The less the dilution, the smaller is the bulk density. If the bulk density of nickel powder should be from 0.7 to 0.9 gram per cc'.,- theconcentration of the carbonyl vapour in the gases introduced into the decomposer'is normally above 75%. Y

Weclaim:

1. Ina process for producing metal powdercharacte'rized by-a' fibrous and hair-like structure and a bulk'density of about 0.3 to 1.3 grams per cubic centimeter by decomposing metal carbonyl vapor, the steps comprising'directing a stream of metal carbonyl vapor of at least 65 concentration adjacent a heated surface maintained at an elevate'ddecomposition temperature of not more than about 400 C. while maintaining said vapor at 'a flo w rate r by a fibrous and hair-like structure and a bulk density of about 0.3 to 1.3 grams per cubic centimeter by decomposing a carbonyl vapor of metal selected from said group, the steps comprising directing a stream of said metal carbonyl vapor of about 65% to 100% concentration adjacent a heated surfacemaintained at an elevated decomposition temperature of not more thanabout 400 C. while maintaining said vapor at a fiow rate equivalent to about 4 to 10 liters of liquid carbonyl per hour per foot of the perimeter'of the heated surface cross section, and causingsaid stream to flow substantially longitudinally along said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the vapor is not more than 15 inches from a heated surface and so that the cross-sectional area of said stream is'at least five square feet and the cross section of said stream a heated surface maintained at an elevated decomposition temperature of not more than about 400 C. while maintaining said vapor at a flow rate equivalent to about 4 to 10 liters of liquid carbonyl per hour per foot of the perimeter of the heated surface cross section, and causing said stream to flow substantially longitudinally along 'said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the vapor is not more than 15 inches from a heated surface and so that the cross-sectional area of said streain is at leastfive square feet and the cross section of said stream defines'a substantially annular configuration, where,- by a substantially uniform commercial product is produced consistently and continuously;

4. In a process for producing metal powder selected from the group consisting of nickel. and iron characterized by a fibrous and hair-like structure and a bulk density of about 0.3v to 1.3 gramsper cubic centimeter by decompos ing a carbonyl vapor of metal selected from said group, the steps comprising directing a stream of said metal carbonyl vapor comprising about 100% carbonyl vapor adjacent a heated surface maintained at an elevated decomposition temperature of not more than about 400" C. whiletrnaintaining said vapor at a flow rateequivalent' to about 4 to '10 liters of liquid carbonyl per hour per foot of the perimeter of the heated surface cross section, and causing said stream to flow substantially longitudinally along said heated surface While controlling the fiow of said stream' during at least the initial part of the decomposition so that the vapor is not more than 15 inches from uniform-commercial product is produced consistently and equivalent to about 4, to 10 litres of liquid carbonyl per 1 hour per foot of the perimeter of the heated surface cross section, and causing said stream to flow-substantially longitudinally along said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the vapor stream is not more than 15 inches from a heated surface and, so that the cross-sectional area of said stream is at least five square feet and the crosssection of said stream is of substantially elongated configuration. 1 a I 2. In a process for producing metal powder selected from the group consisting of nickel and iron characterized continuously.

5. 'In a process for producing nickel powder characterized by a fibrous and hair-like structure and bulk density of about 0.7 to 0.9 gram per cubic centimeter by decomposing nickel carbonyl vapor, the steps comprising directing a stream of nickel carbonyl vapor of above 75% concentration adjacent a heated surface maintained at an elevated decomposition temperature of not more than about 400 C. while maintaining said vapor at a flow rate equivalent to about 4 to 10 liters of liquid carbonyl per tion of said stream is of substantially elongated configuration of substantially constant width, whereby a substantially uniform commercial nickel powder is obtained consistently and continuously.

6. In a process for producing metal powder selected from the group consisting of nickel and iron characterized by a fibrous and hair-like structure and a bulk density of about 0.3 to 1.3 grams per cubic centimeter by decomposing a carbonyl vapor of metal selected from said group, the steps comprising directing a stream of said metal carbonyl vapor of at least 65% concentration adjacent a heated surface maintained at an elevated decomposition temperature of not more than about 400 C. while maintaining said vapor at a flow rate equivalent to about 4 to liters of liquid carbonyl per hour per foot of the perimeter of the heated surface cross section, and

causing said stream to flow substantially longitudinally along said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the vapor is not more than inches from a heated surface and so that the cross-sectional area of said stream is at least five square feet and the cross section of said stream adjacent the heated surface substantially defines a circular annulus having a radial width ranging from about 10 inches to 24 inches, whereby a substantially uniform commercial product is obtained consistently and continuously.

7. In a process for producing nickel powder characterized by a fibrous and hair-like structure and a bulk density of about 0.75 gram per cubic centimeter by decomposing nickel carbonyl vapor, the steps comprising directing a stream of said nickel carbonyl vapor comprising about 100% carbonyl vapor adjacent a heated surface maintained at an elevated decomposition temperature of not more than 400 C. while maintaining said vapor at a flow rate equivalent to about 9.8 liters of liquid carbonyl per hour per foot of the perimeter of the heated surface cross section, and causing said stream to flow substantially longitudinally along said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the cross section of said stream defines a circular annulus having an outside diameter of about 39 inches and an inside diameter of about 13 inches, whereby a substantially uniform commercial nickel powder is obtained consistently and continuously.

8. In a process for producing metal powder selected from the group consisting of nickel and iron characterized by a fibrous and hair-like structure and a bulk density of about 0.3 to 1.3 grams per cubic centimeter by decomposing a carbonyl vapor of metal selected from said group, the steps comprising directing a stream of said metal carbonyl vapor of at least concentration adjacent a heated surface maintained at an elevated decomposition temperature of not more than about 400 C. while maintaining said vapor at a flow rate equivalent to about 4 to 10 liters of liquid carbonyl per hour per foot of the perimeter of the heated surface cross section, and causing said stream to flow substantially longitudinally along said heated surface while controlling the flow of said stream during at least the initial part of the decomposition so that the vapor is not more than 15 inches from a heated surface and so that the cross-sectional area of said stream is greater than five square feet and the cross section of said stream defines a rectangle of substantially elongated configuration having a width not exceeding 30 inches.

9. The process according to claim 8 wherein the width of the rectangle defining the cross section of the vapor stream ranges from about 20 inches to 30 inches.

References Cited in the file of this patent UNITED STATES PATENTS 455,228 Mond June 30, 1891 551,220 Mond Dec. 10, 1895 1,836,732 Schlecht et a1 Dec. 15, 1931 

1. IN A PROCESS FOR PRODUCING METAL POWDER CHARACTERIZED BY A FIBROUS AND HAIR-LIKE STRUCTURE AND A BULK DENSITY OF ABOUT 0.3 TO 1.3 GRAMS PER CUBIC CENTIMETER BY DECOMPOSING METAL CARBONYL VAPOR, THE STEPS CONPRISING DIRECTING A STREAM OF METAL CARBONYL VAPOR OF AT LEAST 65* CONCENTRATION ADJACENT A HEATED SURFACE MAINTAINED AT AN ELEVATED DECOMPOSITION TEMPERATURE OF NOT MORE THAN ABOUT 400* C. WHILE MAINTAINING SAID VAPOR AT A FLOW RATE EQUIVALENT TO ABOUT 4 TO 10 LITRES OF LIQUID CARBONYL PER HOUR PER FOOT OF THE PERIMETER OF THE HEATED SURFACE CROSS SECTION, AND CAUSING SAID STREAM TO FLOW SUBSTANTIALLY LONGITUDINALLY ALONG SAID HEATED SURFACE WHILE CONTROLLING THE FLOW OF SAID STREAM DURING AT LEAST THE INITIAL PART OF THE DECOMPOSITION SO THAT THE VAPOR STREAM IS NOT MORE THAN 15 INCHES FROM A HEATED SURFACE AND SO THAT THE CROSS-SECTIONAL AREA OF SAID STREAM IS AT LEAST FIVE SQUARE FEET AND THE CROSS SECTION OF SAID STREAM IS OF SUBSTANTIALLY ELONGATED CONFIGURATION. 